The system losses account for performance losses you would expect in a real system that are not explicitly calculated by the PVWatts® model equations.
The default value for the system losses of 14% is based on the categories in the table below, and calculated as follows:
100% × [ 1- ( 1 - 0.02 ) × ( 1 - 0.03 ) ×
( 1 - 0.02 ) × ( 1 - 0.02 ) ×
( 1 - 0.005 ) × ( 1 - 0.015) ×
( 1- 0.01 ) × ( 1 - 0.03) ] = 14%
The Inverter's DC-to-AC Conversion Efficiency is a separate input under Advanced Parameters with a default value of 96%. Do not include inverter conversion losses in the system loss percentage.
PVWatts® calculates temperature-related losses as a function of the cell temperature, so you should not include temperature loss in the system loss percentage. See the Technical Reference for details.
If you want to use a value other than the default, you can either type a new value, or use the calculator specify values for the categories listed in the table below. For a description of the categories, see System Losses Categories.
| Category | Default Value (%) |
|---|---|
| Soiling | 2 |
| Shading | 3 |
| Snow | 0 |
| Mismatch | 2 |
| Wiring | 2 |
| Connections | 0.5 |
| Light-Induced Degradation | 1.5 |
| Nameplate Rating | 1 |
| Age | 0 |
| Availability | 3 |